Conventionally, portable electronic systems adopting the wireless LAN, such as notebook-sized personal computers (hereinafter referred to as notebook-sized PCs) and Personal Digital Assistants (PDA) have been used at offices, homes, and the like. Such electronic systems allow users to connect to broadband routers from any places by wireless and to access the Internet freely.
An electronic system as described above is provided with, for example, an internal antenna for transmitting and receiving electric waves inside a housing. In addition, the housing is provided with a coaxial connector having a switching function in order to further increase the receiving efficiency thereof. Accordingly, when it is difficult to transmit and receive electric waves through the internal antenna, the coaxial connector is connected to the external antenna to switch from the internal antenna to the external antenna. Therefore, electric waves can be transmitted and received through the external antenna.
Wireless LAN like this is standardized under IEEE 802.11a by Institute of Electrical and Electronic Engineers (IEEE). More specifically, Federal communications commission (FCC) defines that manufacturers shall customize connectors for wireless LAN for electronic systems to transmit and receive electric waves in a frequency range around 5.2 GHz used for high-speed wireless LAN. In other words, it is defined that connectors for antennas shall each have a maker-specific structure so as to prevent any external antennas of other manufacturers from being connected to the connectors.
The above-described definition presented by FCC is not applied to internal antennas, but the FCC definition is applied to connectors to which external antennas are to be connected. Therefore the connectors must be customized.
In order to solve the problem, there has been known a connector having a key and a key groove (see JP-A-9-306603). More specifically, the connector has a plug connected to an external antenna and a receptacle formed with a plug-in opening in which the plug is to be plugged. Here, the plug has the key provided in its distal end, and the receptacle has the key groove provided in the plug-in opening thereof. According to the configuration, the key of the plug is fitted in the key groove of the receptacle, which makes it impossible to connect the other manufacturer's plug to the receptacle. The plug and receptacle can be reliably connected with each other by screwing the coupling cap nut that the plug holds in the external thread formed in the periphery of the receptacle.
However, it is difficult to identify the location of the key groove in a connector as described above when the receptacle is mounted in a place which is difficult for a user to see. Especially, in recent years notebook-sized PCs have been advancing in slimming the housing and accordingly in downsizing the connectors and as such, it has been more difficult to identify the location of the key groove. Therefore, the plug couldn't be connected to the receptacle readily.
Furthermore, when a coaxial cable is connected to the side face of the plug, i.e. when the connector is a so-called right angle connector (and also referred to as an L-shaped connector) in which the direction of the plug plugged in and the extending direction of the coaxial cable intersect at right angles, the posture of the plug is limited by the provision of the key and key groove when the plug is plugged. Accordingly, the connector may not be able to obtain good usability because the extending direction of the coaxial cable is also limited.
The above-described definition by FCC is not limited to the combination of the key and key groove as a maker-specific structure.